1. Field of the Invention
The present invention is directed to a process for preparing isocyanate-terminated prepolymers from OH-terminated prepolymers based on 4,4'-diisocyanatodicyclohexyl-methane, the products produced therefrom and their use in one-component, moisture-cure systems or as the isocyanate component in two-component polyurethanes.
2. Description of the Prior Art
The use of isocyanate-terminated prepolymers as one-component, moisture-cure polyurethanes or as the isocyanate-component in two-component polyurethanes is known as disclosed by U.S. Pat. Nos. 4,211,804, 4,273,912, 4,247,675, 4,292,350, 4,254,168, 4,282,123, 4,195,009 and 4,184,005. In the production of light stable and flexible polyurethane coatings, it is also known that the use of isocyanate-terminated prepolymers prepared from an isocyanate component based exclusively on 4,4'-diisocyanato-dicyclohexyl-methane provide enhanced flexibility, high abrasion resistance and good hydrolytic stability. However, when these isocyanate-terminated prepolymers are produced using normal preparation procedures, they suffer from the disadvantage of containing high amounts of unreacted diisocyanate (free monomer). These contents are normally greater than 2% by weight and sometimes exceed 10% by weight. Due to the high free monomer content of these prepolymers, they may create certain handling and application problems (e.g. in spray applications).
Accordingly, it is an object of the present invention to provide isocyanate-terminated prepolymers containing urethane groups based on 4,4'-diisocyanato-dicyclohexyl-methane and which contain less than about 2% by weight of unreacted diisocyanates.
It is a further object of the present invention to provide isocyanate-terminated prepolymers containing urethane groups based on 4,4'-diisocyanato-dicyclohexyl-methane which are suitable and safer to handle in various application areas, e.g. for spray applications, when used in one-component, moisture-cure systems or as the isocyanate component in two-component polyurethane systems.
It is an additional object of the present invention to use isocyanate-terminated prepolymers containing urethane groups based on 4,4'-diisocyanato-dicyclohexyl-methane to prepare polyaddition products which possess enhanced flexibility, high abrasion resistance and good hydrolytic stability.